Straight chrome stainless steel pressure vessel



Jun 6, 1956 c. s. WALTON STRAIGHT CHROME STAINLESS STEEL PRESSURE VESSELFiled 001:. l, 1952 M Kr a mwwmwwm Imam: (4e: 5 14 41 ra/v, fimzw/dwUnited States Patent STRAIGHT CHROlVIE STAINLESS STEEL PRESSURE VESSELCarl S. Walton, Sewickley, Pa., assignor to United States SteelCorporation, a corporation of New Jersey Application October 1, 1952,Serial No. 312,511

3 Claims. (Cl. 75-126) This invention relates to straight chromestainless steels and more particularly to a stainless steel of the 27%chromium grade which is substantially free from embrittlement afterprolonged holding at high temperatures.

Straight chromium, ferritic, stainless steel of the so called 27% grade,i. e., containing 24 to 30% chromium has excellent resistance tooxidation up to temperatures of 2000 F. However, this steel cannot beused in many applications which involve protracted heating attemperatures from 1000 to 1300 F. due to embrittlement caused byformation of the intermetallic compound of the iron chromium systemknown as the sigma phase. While this can be overcome by annealing attemperatures over 1600 F. such annealing is impractical for manyarticles such as pressure vessels and the like.

It is accordingly an object of this present invention to provide astraight chrome steel of the 27% chrome grade which is free fromembrittlement after prolonged heating at temperatures over 1000 F.

The foregoing and further objects will be apparent from the followingspecification when read in conjunction with the attached drawing,wherein the single figure is a graph depicting the embrittling effect ofsilicon on 27% chromium straight chromium stainless steel.

Straight chromium stainless steel of the 27% chromium type generallycontains 24 to 30% chromium and .35% maximum carbon, along with 1.00%maximum man ganese, .04% maximum phosphorus, .03% maximum sulphur, .25maximum nitrogen and between about .35 to 1.00% silicon. I havediscovered that by formulating the steel With the least possible siliconand preferably less than .17% maximum silicon that the formation ofsigma phase and resulting embrittlement when heated for long periods inthe 1000 to 1300 F. range can be completely overcome.

In accordance with this invention, a number of long time temperatureexperiments comprising holding steels of the foregoing composition andalong with steels higher silicon contents at temperatures of 1050 and1200 F. for 10,000 hours were conducted. The results, so far as hardnessand the Rockwell scale, were substantially the "ice same at bothtemperatures so that they are depicted by a single line on the graph ofthe drawing. This shows conclusively that with silicon contents lessthan about .17%, no change in hardness results from prolonged heating at1050 and 1200" F. It is also apparent that increasing the silicon up toabout .27% causes a rapid increase in Brinell hardness but thereabovethe hardness remains substantially constant.

A typical steel embodying the teachings of this invention contains .12%carbon, .63% manganese, 27.48% chromium and .O9% silicon along with.014% phosphorus, .O1% sulphur and .08% residual nickel.

While I have shown and described a single embodiment of my invention, itwill be understood that this embodiment is merely for the purpose ofillustration and description and that various other forms may be devisedWithin the scope of my invention, as defined in the appended claims.

I claim:

1. A pressure vessel of the type subjected in use to prolonged heatingin the temperature range of 1000 to 1300 F. formed of ferritic straightchromium stainless steel containing between .03 and 35% carbon, 24 to30% chromium, 1.00% maximum manganese, and less than .17% silicon, saidpressure vessel being characterized by substantially complete freedomfrom sigma phase embrittlement after being heated for 10,000 hours inthe temperature range of 1000 to 1300 F.

2. The method of inhibiting sigma phase embrittlement in pressurevessels subjected to prolonged heating in the temperature range of 1000to 1300 F. comprising producing straight chromium stainless steelcontaining between 24 and 30% chromium, .03 to 35% carbon, which type ofsteel is subject to the formation of sigma phase on prolonged heating insaid temperature range and inhibiting the formation of such phase bylimiting the silicon content of said steel to less than .17%, forming apressure vessel therefrom and heating said vessel for 10,000 hours inthe range of 1000 to 1300 F., said vessel being characterized after suchheating by the substantially complete freedom from sigma phaseembrittlement.

3. A pressure vessel of the type subjected in use to prolonged heatingin the temperature range of 1000 to 1300 F. formed of ferritic straightchromium stainless steel containing about .12% carbon, about .63%manganese, about 27.48% chromium and about .09% silicon with the balanceiron and residual impurities, said pressure vessel being characterizedby substantially complete freedom from sigma phase embrittlement afterbeing heated for 10,000 hours in the temperature range of 1000 to 1300F.

References Cited in the file of this patent Metals and Alloys, vol. 7,August 1936, pages 207-210. Comptes Rendus, vol. 226, June 1948, pages2150-2151.

1. A PRESSURE VESSEL OF THE TYPE SUBJECTED IN USE TO PROLONGED HEATINGIN THE TEMPERATURE RANGE OF 1000 TO 1300* F. FORMED OF FERRITIC STRAIGHTCHROMIUM STAINLESS STEEL CONTAINING BETWEEN .03 AND .35% CARBON, 24 TO30% CHROMIUM, 1.00% MAXIMUM MANGANESE, AND LESS THAN .17% SILICON, SAIDPRESSURE VESSEL BEING CHARACTERIZED BY SUBSTANTIALLY COMPLETE FREEDOMFROM SIGMA PHASE EMBRIT-